What happened
During a training session involving a student pilot and a contract instructor, an aircraft experienced repeated engine failures during the initial startup phase. After two unsuccessful attempts to maintain engine operation, the engines were started a third time, and the aircraft began its takeoff roll. Shortly after the roll commenced, the pilot reported an unspecified issue with one of the engines. The aircraft subsequently veered across a median and onto a parallel runway, where it rolled sharply to the right, struck the ground, and underwent a cartwheel motion. At the time of the impact, the landing gear was extended, and the propellers had not been feathered.
Findings
Investigations into the mechanical state of the engines revealed that while the right engine and turbocharger showed no abnormalities, the left engine contained significant internal defects. Specifically, the throttle valve and mixture shaft within the fuel control assembly were jammed in the idle rpm and idle cutoff positions. Further testing of the manifold valve and fuel injector lines indicated higher-than-normal pressures, suggesting a flow restriction.
Upon disassembly of the manifold valve, investigators found that the needle valve in the plunger assembly was stuck in the fully open position, which had caused the needle valve spring to collapse. Subsequent examination of the plunger revealed that the threads had been improperly tapped inside the retainer, and metal shavings were discovered between the retainer and the spring. It was noted that the Teledyne Continental Motor (TCM) retainer is designed without threads. Data from the GPS indicated that the aircraft traveled 2,698 feet before reaching rotation speed, with a maximum speed of 132 mph. Calculations showed that the distance required to clear a 50-foot obstacle on a single engine was 2,600 feet, while the available distance to clear such an obstacle was insufficient given the actual takeoff performance.